Strobiluron Fungicide Greening Effects on Soybeans in Alabama, 2006 and 2007: Application Timing and Desiccants

D.P. Delaney1, E. J. Sikora 2, M.A. Delaney 2, K.S. Lawrence 2 , R. Dawkins3, R. Durbin3, and B. Norris3

1Dept. of Agronomy & Soils, 2Dept. of Entomology & Plant Pathology, 3AL Ag Experiment StationAuburn University, Alabama

IntroductionUse of strobiluron fungicides is relatively new to Alabama producers; however up to 50% of the soybean acreage was treated in 2005, due to the presence of Asian Soybean Rust (ASR). Many of these fields experienced retention of green leaves long after pod maturity in 2005, but was highly variable.Differences were observed according to cultivars, use of different active ingredients and rates, timing and weather. Many soybean producers delayed harvest until frost or weathering removed these leaves, leading to seed deterioration and shattering losses. Others combined through fields which had large amounts of green leaves and stems, but at greatly reduced speeds and with increased fuel and machinery costs and foreign material dockage. Desiccant materials may dry up these green leaves and stems for more timely and efficient harvest, but have been little used in Alabama soybean production. A series of experiments was conducted across the state in 2006 and 2007 to investigate the effects of timing of strobiluron fungicide applications on retention of green leaves and stems, and of harvest aid treatments to alleviate effects.

MethodsStrobiluron Effects: Three trials investigated strobiluron timing at

different growth stages, with and without desiccants applied to increase harvest efficiency. Trials were conducted in north and central AL at the Tennessee Valley RREC (TVS), Sand Mountain RREC (SMS), and the EV Smith Field Crops Unit (EVS). Headline® (pyraclostrobin) @ 6 fl. oz/A was applied at R1, R3, and/or R5 in factorial combinations with or without desiccation. Only the EVS location was irrigated, however, its effects were limited due to water availability and hot and dry weather. A tank mix of Gramoxone Inteon® 2L (paraquat) @ 1 pt/A plus sodium chlorate @ 3 lb a.i. /A was applied to half the plots at pod maturity. All treatments wereapplied with flat fan nozzles in a volume of 18 - 20 gpa. Desiccated treatments were harvested 10 to 15 days after treatment (DAT), while non-desiccated plots were harvested after natural leaf drop (10 to 21 days later). Grain yield andharvest moisture data was recorded. Seed samples were also analyzed for foreign matter content and seed weight.

Desiccation materials: Three trials investigated the use of different harvest aid materials and combinations to alleviate leaf greening effects. Trials were conducted at SMS, EVS, and the Gulf Coast RREC (GCS). Test areas had three applications of Headline @ 6 to 9 fl oz./A at R1, R3, and R5 to attempt to trigger greening effects. At pod maturity, ten harvest aid materials were applied with flat fan nozzles in a volume of 18 - 20 gpa. Trials were rated at 4 and 7 DAT, and harvested at 10 to 15 DAT. Grain yield and harvest moisture data was recorded. Seed samples were also analyzed for foreign matter content and seed weight.

Data was analysed at p=0.10

ResultsThe 2006 and 2007 growing seasons were extremely dry in most of AL. Strobiluron greening effects were much reduced in 2006 and 2007, compared to 2005. In 2006, only 1 of 3 locations recorded greening differences between strobiluron application timings. At TVS, leaf greening was significantly increased by strobiluron applications at R1, R3, and R1+R3 compared to untreated plots and applications at R5 and R3+R5. Harvested grain yield not affected by fungicide application at any location, but was increased by desiccation at all locations with an average of increase of 2.6 bu/A. Total moisture contentwas reduced from 16.3 to 12.7 % at TVS, while it was unaffected by fungicide or desiccation at other locations. Trash and seed weight was little affected by treatments, although small differences were noted at EVS for fungicide application timing on 100-seed weights.In 2007, no significant differences were recorded between fungicide timing treatments for greening, yield or 100-seed weights. In contrast to 2006, Desiccation treatments increased yield at only one location in 2007, by 5.2 bu/A at EVS.Leaf greening effects were also reduced in the Desiccation Materials trials, with the GCS location abandoned due to nearly complete leaf shed before treatments. All treatments increasedleaf desiccation 4 and 10 days at EVS and at 10 DAT at SMS. At SMS at 4 DAT, all treatments except Aim + crop oil increased leaf desiccation. Several treatments reduced total harvest moisture at EVS and SMS compared to the check. Treatments which included paraquat (Gramoxone Inteon, Firestorm®) or sodium chlorate as active ingredients were most effective in reducing harvest moisture. Harvested grain yield was significantly increased by three treatments at EVS, but not at SMS. There was no significant difference in trash content or seed weights between any treatments. In 2007, the GCS location was again abandoned due to complete leaf shed. No significant yield, grain moisture, or seed weight differences were recorded at EVS or SMS in 2007.

AcknowledgementsThe support of the Alabama Soybean Producers through checkoff funds, staff of the Alabama Agricultural Experiment Stations, and private industry sources of seed and materials is gratefully acknowledged.

Conclusions. In contrast to the 2005 growing season, very little effect of

strobiluron fungicides on extended leaf greening was noted in 2006 or 2007 in Alabama. At one location in 2006, increased strobiluron greening effects were noted with early applications of fungicide (R1 to R3). At this location only, grain moisture content was also reduced by desiccation.

Several desiccant materials and combinations increased leaf desiccation and decreased harvest moisture compared to check treatments, and yield was also increased at one location.

In all trials, trash content and seed weights were little affected by strobiluron fungicide applications or desiccant treatments.

Green leaves and stems retained after pod maturity

Coastal Plain

Black Belt Prairie

Piedmont

Limestone Valley

Locations of Strobiluron Greening and Desiccant Trials, 2006 and 2007

EVS

GCS

SMSTVS

Strobiluron Fungicide Effects on Soybeans, EVS, SMS and TVS, 2006

0

5

10

15

20

25

30

35

40

bu/A

EVS SMS TVS

NoDesiccant

Desiccant

Soybean Yield

LSD (0.10) = 3.0

LSD(0.10) = 2.1

LSD (0.10) = 2.4 Desiccation Materials for Soybeans, EVS 2006

0123456789

10

10 =

dry

3 Days 10Days

Untreated Check

Inteon +NIS, 1/8 lb

Inteon +NIS, 1/4 lb =(1 pt)Inteon +NIS, 1/2 lb

Inteon +NIS, 1/4 lb +Sod Chl 3 lbSodium Chlorate 6 lb

Firestorm +NIS, 1/4 lb

Aim @ 1.4 fl oz + COC

Aim @ 1.4 fl oz +Inteon @1/8 lb + COCAim @ 1.4 fl oz +Roundup WM @22oz

Leaf Desiccation

Desiccation Materials for Soybeans, SMS, 2006

0123456789

10

10 =

dry

3 Days 10Days

Untreated Check

Inteon +NIS, 1/8 lb

Inteon +NIS, 1/4 lb =(1 pt)Inteon +NIS, 1/2 lb

Inteon +NIS, 1/4 lb +Sod Chl 3 lbSodium Chlorate 6 lb

Firestorm +NIS, 1/4 lb

Aim @ 1.4 fl oz + COC

Aim @ 1.4 fl oz +Inteon @1/8 lb + COCAim @ 1.4 fl oz +Roundup WM @22oz

Leaf Desiccation

Strobiluron Fungicide Effects on Soybeans, EVS, SMS and TVS, 2007

0

10

20

30

40

50

60

70

bu/A

EVS SMS TVS

NoDesiccant

Desiccant

Soybean Yield

LSD (0.10) = NS

LSD(0.10) = 2.0

LSD (0.10) = NS